I have a bit a problem. I recently bought a house. The house is approx 38 years old. We redid one bathroom and then realized that the warm water pressure is too low. On recommendation of the plumber we replaced the old 100kpa geyser with a Franke 150l 400kpa geyser. The geyser has three overflows (drain pan, security valve and pressure valve). After installation, we had the problem that the pressure valve shot out (not only drip) water every time we opened warm and cold in the shower (or any other tap). The plumbers then said that the problem is the immensely high cold water pressure in the area. He said the cold water is pushing back the hot water and that causes the pressure valve to overflow. They then removed the pressure valve out of the ceiling and put it in the garden after the meter. The setup is now municipal tap, meter, my tap, pressure valve. Now the whole house is balanced on 400kpa (its a 400kpa pressure valve), however when I want to water my garden its impractical as 400kpa is too low for a 30m hose pipe. I don't know what else to do. Do you guys have any idea?